IWYU: include cstdint in register_context.h as it uses uintptr_t

GCC build fix as build fails with this:
../../base/profiler/register_context.h:31:1: error: ‘uintptr_t’ does not name a type; did you mean ‘intptr_t’?
 uintptr_t& AsUintPtr(T* value) {
 ^~~~~~~~~
 intptr_t
../../base/profiler/register_context.h:110:3: error: ‘uintptr_t’ does not name a type; did you mean ‘intptr_t’?
   uintptr_t stack_pointer;
   ^~~~~~~~~
   intptr_t
../../base/profiler/register_context.h:111:3: error: ‘uintptr_t’ does not name a type; did you mean ‘intptr_t’?
   uintptr_t frame_pointer;
   ^~~~~~~~~
   intptr_t
../../base/profiler/register_context.h:112:3: error: ‘uintptr_t’ does not name a type; did you mean ‘intptr_t’?
   uintptr_t instruction_pointer;
   ^~~~~~~~~
   intptr_t
../../base/profiler/register_context.h:115:8: error: ‘uintptr_t’ does not name a type; did you mean ‘intptr_t’?
 inline uintptr_t& RegisterContextStackPointer(RegisterContext* context) {
        ^~~~~~~~~
        intptr_t
../../base/profiler/register_context.h:119:8: error: ‘uintptr_t’ does not name a type; did you mean ‘intptr_t’?
 inline uintptr_t& RegisterContextFramePointer(RegisterContext* context) {
        ^~~~~~~~~
        intptr_t
../../base/profiler/register_context.h:123:8: error: ‘uintptr_t’ does not name a type; did you mean ‘intptr_t’?
 inline uintptr_t& RegisterContextInstructionPointer(RegisterContext* context) {
        ^~~~~~~~~
        intptr_t

Bug: 819294
Change-Id: I49567b00a6f021686c52053a22fb9c502c84f1bc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1879908Reviewed-by: Mike Wittman <wittman@chromium.org>
Commit-Queue: José Dapena Paz <jose.dapena@lge.com>
Cr-Commit-Position: refs/heads/master@{#709398}

base/profiler/register_context.h

@@ -9,6 +9,7 @@
 #ifndef BASE_PROFILER_REGISTER_CONTEXT_H_
 #define BASE_PROFILER_REGISTER_CONTEXT_H_
 
+#include <cstdint>
 #include <type_traits>
 
 #include "build/build_config.h"